Microglia dictate the impact of saturated fat consumption on hypothalamic inflammation and neuronal function

Interleukin-2 improves insulin sensitivity through hypothalamic sympathetic activation in obese mice

BACKGROUND

IL-2 regulates T cell differentiation: low-dose IL-2 induces immunoregulatory Treg differentiation, while high-dose IL-2 acts as a potent activator of cytotoxic T cells and NK cells. Therefore, high-dose IL-2 has been studied for use in cancer immunotherapy. We aimed to utilize low-dose IL-2 to treat inflammatory diseases such as obesity and insulin resistance, which involve low-grade chronic inflammation.

MAIN BODY

Systemic administration of low-dose IL-2 increased Treg cells and decreased inflammation in gonadal white adipose tissue (gWAT), leading to improved insulin sensitivity in high-fat diet-fed obese mice. Additionally, central administration of IL-2 significantly enhanced insulin sensitivity through the activation of the sympathetic nervous system. The sympathetic signaling induced by central IL-2 administration not only decreased interferon γ (IFNγ) + Th1 cells and the expression of pro-inflammatory cytokines, including Il-1β, Il-6, and Il-8, but also increased CD4 + CD25 + FoxP3 + Treg cells and Tgfβ expression in the gWAT of obese mice. These phenomena were accompanied by hypothalamic microgliosis and activation of pro-opiomelanocortin neurons. Furthermore, sympathetic denervation in gWAT reversed the enhanced insulin sensitivity and immune cell polarization induced by central IL-2 administration.

CONCLUSION

Overall, we demonstrated that IL-2 improves insulin sensitivity through two mechanisms: direct action on CD4 + T cells and via the neuro-immune axis triggered by hypothalamic microgliosis.

Trapped fat: Obesity pathogenesis as an intrinsic disorder in metabolic fuel partitioning

Our understanding of the pathophysiology of obesity remains at best incomplete despite a century of research. During this time, two alternative perspectives have helped shape thinking about the etiology of the disorder. The currently prevailing view holds that excessive fat accumulation results because energy intake exceeds energy expenditure, with excessive food consumption being the primary cause of the imbalance. The other perspective attributes the initiating cause of obesity to intrinsic metabolic defects that shift fuel partitioning from pathways for mobilization and oxidation to those for synthesis and storage. The resulting reduction in fuel oxidation and trapping of energy in adipose tissue drives a compensatory increase in energy intake and, under some conditions, a decrease in expenditure. This theory of obesity pathogenesis has historically garnered relatively less attention despite its pedigree. Here, we present an updated comprehensive formulation of the fuel partitioning theory, focused on evidence gathered over the last 80 years from major animal models of obesity showing a redirection of fuel fluxes from oxidation to storage and accumulation of excess body fat with energy intake equal to or even less than that of lean animals. The aim is to inform current discussions about the etiology of obesity and by so doing, help lay new foundations for the design of more efficacious approaches to obesity research, treatment and prevention.

Voluntary exercise suppresses inflammation and improves insulin resistance in the arcuate nucleus and ventral tegmental area in mice on a high-fat diet

A high-fat diet (HFD) causes inflammation with an increase in microglial activity in the hypothalamic arcuate nucleus (ARC) and ventral tegmental area (VTA), resulting in insulin resistance in both regions. This leads to a deterioration in glucose and energy metabolism. The effect of voluntary exercise on HFD-induced inflammation in the central nervous system (CNS) remains unclear. To clarify the effects of voluntary exercise on the CNS, 8-week-old male C57BL6 mice were fed a chow diet (CHD) or HFD for 4 weeks; each group was further divided into running exercise (EX+) on a wheel and no exercise (EX-) groups. The expression of the inflammatory cytokine, tumor necrosis factor alpha (TNFα), in the ARC and VTA was significantly increased in the HFD/EX- group, with an increase of microglial activity noted, compared to the CHD/EX- group. The expression of TNFα was significantly suppressed, with a decrease of microglial activity, in the HFD/EX+ compared to HFD/EX- group. Insulin resistance in the ARC and VTA was improved with the suppression of TNFα expression. The HFD/EX- group showed significant weight gain and impaired glucose metabolism compared to the CHD/EX- group. The HFD/EX+ group showed an improvement in glucose and energy metabolism compared to the HFD/EX- group. In addition, voluntary wheel running suppressed HFD-induced inflammation in the ARC, with a decrease in microglial activity observed independently of weight changes. Our data suggest that voluntary exercise prevents obesity and improves glucose metabolism by suppressing inflammation in the ARC and VTA under HFD conditions.

Hypothalamic Gliosis is Associated With Multiple Cardiovascular Disease Risk Factors

Background

Hypothalamic gliosis is mechanistically linked to obesity and insulin resistance in rodent models. We tested cross-sectional associations between radiologic measures of hypothalamic gliosis in humans and clinically relevant cardiovascular disease risk factors, as well as prevalent coronary heart disease.

Methods

Using brain MRI images from Framingham Heart Study participants (N=867; mean age, 55 years; 55% females), T2 signal intensities were extracted bilaterally from the region of interest in the mediobasal hypothalamus (MBH) and reference regions in the amygdala (AMY) and putamen (PUT). T2 signal ratios were created in which greater relative T2 signal intensity suggests gliosis. The primary measure compared MBH to AMY (MBH/AMY); a positive control ratio (MBH/PUT) also assessed MBH whereas a negative control (PUT/AMY) did not. Outcomes were BMI, HDL-C, LDL-C, fasting triglycerides, and the presence of hypertension (n=449), diabetes mellitus (n=66), metabolic syndrome (n=254), or coronary heart disease (n=25). Dietary risk factors for gliosis were assessed in a prospective analysis. Statistical testing was performed using linear or logistic regression.

Results

Greater MBH/AMY T2 signal ratios were associated with higher BMI (β = 21.5 [95% CI, 15.4- 27.6]; P <0.001), higher fasting triglycerides (β = 1.1 [95% CI, 0.6-1.7]; P <0.001), lower HDL-C (β = -20.8 [95% CI, -40.0 to -1.6]; P =0.034), and presence of hypertension (odds ratio, 1.2 [95% CI, 1.1-1.4]; P =0.0088), and the latter two were independent of BMI. Findings for diabetes mellitus were mixed and attenuated by adjusting for BMI. Metabolic syndrome was associated with MBH/AMY T2 signal ratios (odds ratio, 1.3 [95% CI, 1.1-1.6]; P <0.001). Model results were almost uniformly confirmed by the positive control ratios, whereas negative control ratios that did not test the MBH were unrelated to any outcomes (all P ≥0.05). T2 signal ratios were not associated with prevalent coronary heart disease (all P >0.05), but confidence intervals were wide. Self-reported percentages of macronutrient intake were not consistently related to future T2 signal ratios.

Conclusions

Using a well-established study of cardiovascular disease development, we found evidence linking hypothalamic gliosis to multiple cardiovascular disease risk factors, even independent of adiposity. Our results highlight the need to consider neurologic mechanisms to understand and improve cardiometabolic health.

Microglia in physiological conditions and the importance of understanding their homeostatic functions in the arcuate nucleus

Microglia are highly dynamic cells that have been mainly studied under pathological conditions. The present review discusses the possible implication of microglia as modulators of neuronal electrical responses in physiological conditions and hypothesizes how these cells might modulate hypothalamic circuits in health and during obesity. Microglial cells studied under physiological conditions are highly diverse, depending on the developmental stage and brain region. The evidence also suggests that neuronal electrical activity modulates microglial motility to control neuronal excitability. Additionally, we show that the expression of genes associated with neuron-microglia interaction is down-regulated in obese mice compared to control-fed mice, suggesting an alteration in the contact-dependent mechanisms that sustain hypothalamic arcuate-median eminence neuronal function. We also discuss the possible implication of microglial-derived signals for the excitability of hypothalamic neurons during homeostasis and obesity. This review emphasizes the importance of studying the physiological interplay between microglia and neurons to maintain proper neuronal circuit function. It aims to elucidate how disruptions in the normal activities of microglia can adversely affect neuronal health.

Age and duration of obesity modulate the inflammatory response and expression of neuroprotective factors in mammalian female brain

Obesity has become a global epidemic and is associated with comorbidities, including diabetes, cardiovascular, and neurodegenerative diseases, among others. While appreciable insight has been gained into the mechanisms of obesity-associated comorbidities, effects of age, and duration of obesity on the female brain remain obscure. To address this gap, adolescent and mature adult female mice were subjected to a high-fat diet (HFD) for 13 or 26 weeks, whereas age-matched controls were fed a standard diet. Subsequently, the expression of inflammatory cytokines, neurotrophic/neuroprotective factors, and markers of microgliosis and astrogliosis were analyzed in the hypothalamus, hippocampus, and cerebral cortex, along with inflammation in visceral adipose tissue. HFD led to a typical obese phenotype in all groups independent of age and duration of HFD. However, the intermediate duration of obesity induced a limited inflammatory response in adolescent females' hypothalamus while the hippocampus, cerebral cortex, and visceral adipose tissue remained unaffected. In contrast, the prolonged duration of obesity resulted in inflammation in all three brain regions and visceral adipose tissue along with upregulation of microgliosis/astrogliosis and suppression of neurotrophic/neuroprotective factors in all brain regions, denoting the duration of obesity as a critical risk factor for neurodegenerative diseases. Importantly, when female mice were older (i.e., mature adult), even the intermediate duration of obesity induced similar adverse effects in all brain regions. Taken together, our findings suggest that (1) both age and duration of obesity have a significant impact on obesity-associated comorbidities and (2) early interventions to end obesity are critical to preserving brain health.

The immunology of sickness metabolism

Everyone knows that an infection can make you feel sick. Although we perceive infection-induced changes in metabolism as a pathology, they are a part of a carefully regulated process that depends on tissue-specific interactions between the immune system and organs involved in the regulation of systemic homeostasis. Immune-mediated changes in homeostatic parameters lead to altered production and uptake of nutrients in circulation, which modifies the metabolic rate of key organs. This is what we experience as being sick. The purpose of sickness metabolism is to generate a metabolic environment in which the body is optimally able to fight infection while denying vital nutrients for the replication of pathogens. Sickness metabolism depends on tissue-specific immune cells, which mediate responses tailored to the nature and magnitude of the threat. As an infection increases in severity, so do the number and type of immune cells involved and the level to which organs are affected, which dictates the degree to which we feel sick. Interestingly, many alterations associated with metabolic disease appear to overlap with immune-mediated changes observed following infection. Targeting processes involving tissue-specific interactions between activated immune cells and metabolic organs therefore holds great potential for treating both people with severe infection and those with metabolic disease. In this review, we will discuss how the immune system communicates in situ with organs involved in the regulation of homeostasis and how this communication is impacted by infection.

Microglia in Microbiota-Gut-Brain Axis: A Hub in Epilepsy

There is growing concern about the role of the microbiota-gut-brain axis in neurological illnesses, and it makes sense to consider microglia as a critical component of this axis in the context of epilepsy. Microglia, which reside in the central nervous system, are dynamic guardians that monitor brain homeostasis. Microglia receive information from the gut microbiota and function as hubs that may be involved in triggering epileptic seizures. Vagus nerve bridges the communication in the axis. Essential axis signaling molecules, such as gamma-aminobutyric acid, 5-hydroxytryptamin, and short-chain fatty acids, are currently under investigation for their participation in drug-resistant epilepsy (DRE). In this review, we explain how vagus nerve connects the gut microbiota to microglia in the brain and discuss the emerging concepts derived from this interaction. Understanding microbiota-gut-brain axis in epilepsy brings hope for DRE therapies. Future treatments can focus on the modulatory effect of the axis and target microglia in solving DRE.

A high-fat diet influences neural stem and progenitor cell environment in the medulla of adult mice

It has been widely established that neural stem cells (NSCs) exist in the adult mammalian brain. The area postrema (AP) and the ependymal cell layer of the central canal (CC) in the medulla were recently identified as NSC niches. There are two types of NSCs: astrocyte-like cells in the AP and tanycyte-like cells in the CC. However, limited information is currently available on the characteristics and functional significance of these NSCs and their progeny in the AP and CC. The AP is a part of the dorsal vagal complex (DVC), together with the nucleus of the solitary tract (Sol) and the dorsal motor nucleus of the vagus (10 N). DVC is the primary site for the integration of visceral neuronal and hormonal cues that act to inhibit food intake. Therefore, we examined the effects of high-fat diet (HFD) on NSCs and progenitor cells in the AP and CC. Eight-week-old male mice were fed HFD for short (1 week) and long periods (4 weeks). To detect proliferating cells, mice consecutively received intraperitoneal injections of BrdU for 7 days. Brain sections were processed with immunohistochemistry using various cell markers and BrdU antibodies. Our data demonstrated that adult NSCs and neural progenitor cells (NPCs) in the medulla responded more strongly to short-term HFD than to long-term HFD. HFD increased astrocyte density in the Sol and 10 N, and increased microglial/macrophage density in the AP and Sol. Furthermore, long-term HFD induced mild inflammation in the medulla, suggesting that it affected the proliferation of NSCs and NPCs.

Microglia are Required for Developmental Specification of AgRP Innervation in the Hypothalamus of Offspring Exposed to Maternal High Fat Diet During Lactation

Nutritional fluctuations that occur early in life dictate metabolic adaptations that will affect susceptibility to weight gain and obesity later in life. The postnatal period in mice represents a time of dynamic changes in hypothalamic development and maternal consumption of a high fat diet during the lactation period (MHFD) changes the composition of milk and leads to enhanced susceptibility to obesity in offspring. Agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus (ARH) react to changes in multiple metabolic signals and distribute neuroendocrine information to other brain regions, such as the paraventricular hypothalamic nucleus (PVH), which is known to integrate a variety of signals that regulate body weight. Development of neural projections from AgRP neurons to the PVH occurs during the lactation period and these projections are reduced in MHFD offspring, but underlying developmental mechanisms remain largely unknown. Microglia are the resident immune cells of the central nervous system and are involved in refinement of neural connections and modulation of synaptic transmission. Because high fat diet exposure causes activation of microglia in adults, a similar activation may occur in offspring exposed to MHFD and play a role in sculpting hypothalamic feeding circuitry. Genetically targeted axonal labeling and immunohistochemistry were used to visualize AgRP axons and microglia in postnatal mice derived from MHFD dams and morphological changes quantified. The results demonstrate regionally localized changes to microglial morphology in the PVH of MHFD offspring that suggest enhanced surveillance activity and are temporally restricted to the period when AgRP neurons innervate the PVH. In addition, axon labeling experiments confirm a significant decrease in AgRP innervation of the PVH in MHFD offspring and provide direct evidence of synaptic pruning of AgRP inputs to the PVH. Microglial depletion with the Colony-stimulating factor 1 receptor inhibitor PLX5622 determined that the decrease in AgRP innervation observed in MHFD offspring is dependent on microglia, and that microglia are required for weight gain that emerges as early as weaning in offspring of MHFD dams. However, these changes do not appear to be dependent on the degree of microglial mediated synaptic pruning. Together, these findings suggest that microglia are activated by exposure to MHFD and interact directly with AgRP axons during development to permanently alter their density, with implications for developmental programming of metabolic phenotype.

Rethinking the role of microglia in obesity

Microglia are the macrophages of the central nervous system (CNS), implying their role in maintaining brain homeostasis. To achieve this, these cells are sensitive to a plethora of endogenous and exogenous signals, such as neuronal activity, cellular debris, hormones, and pathological patterns, among many others. More recent research suggests that microglia are highly responsive to nutrients and dietary variations. In this context, numerous studies have demonstrated their significant role in the development of obesity under calorie surfeit. Because many reviews already exist on this topic, we have chosen to present the state of our reflections on various concepts put forth in the literature, bringing a new perspective whenever possible. Our literature review focuses on studies conducted in the arcuate nucleus of the hypothalamus, a key structure in the control of food intake. Specifically, we present the recent data available on the modifications of microglial energy metabolism following the consumption of an obesogenic diet and their consequences on hypothalamic neuron activity. We also highlight the studies unraveling the mechanisms underlying obesity-related sexual dimorphism. The review concludes with a list of questions that remain to be addressed in the field to achieve a comprehensive understanding of the role of microglia in the regulation of body energy metabolism. This article is part of the Special Issue on "Microglia".

High-intensity interval training improves hypothalamic inflammation by suppressing HIF-1α signaling in microglia of male C57BL/6J mice

Repeated bouts of high-intensity interval training (HIIT) induce an improvement in metabolism via plasticity of melanocortin circuits and attenuated hypothalamic inflammation. HIF-1α, which plays a vital role in hypothalamus-mediated regulation of peripheral metabolism, is enhanced in the hypothalamus by HIIT. This study aimed to investigate the effects of HIIT on hypothalamic HIF-1α expression and peripheral metabolism in obese mice and the underlying molecular mechanisms. By using a high-fat diet (HFD)-induced obesity mouse model, we determined the effect of HIIT on energy balance and the expression of the hypothalamic appetite-regulating neuropeptides, POMC and NPY. Moreover, hypothalamic HIF-1α signaling and its downstream glycolytic enzymes were explored after HIIT intervention. The state of microglia and microglial NF-κB signaling in the hypothalamus were also examined in vivo. In vitro by using an adenovirus carrying shRNA-HIF1β, we explored the impact of HIF-1 signaling on glycolysis and NF-κB inflammatory signaling in BV2 cells. Food intake was suppressed and whole-body metabolism was improved in exercised DIO mice, accompanied by changes in the expression of POMC and NPY. Moreover, total and microglial HIF-1α signaling were obviously attenuated in the hypothalamus, consistent with the decreased levels of glycolytic enzymes. Both HFD-induced microglial activation and hypothalamic NF-κB signaling were significantly suppressed following HIIT in vivo. In BV2 cells, after HIF-1 complex knockdown, glycolysis and NF-κB inflammatory signaling were significantly attenuated. The data indicate that HIIT improves peripheral metabolism probably via attenuated HFD-induced microglial activation and microglial NF-κB signaling in the hypothalamus, which could be mediated by suppressed microglial HIF-1α signaling.

Vagus Nerve and Gut-Brain Communication

The vagus nerve, as an important component of the gut-brain axis, plays a crucial role in the communication between the gut and brain. It influences food intake, fat metabolism, and emotion by regulating the gut-brain axis, which is closely associated with the development of gastrointestinal, psychiatric, and metabolism-related disorders. In recent years, significant progress has been made in understanding the vagus-mediated regulatory pathway, highlighting its profound implications in the development of many diseases. Here, we summarize the latest advancements in vagus-mediated gut-brain pathways and the novel interventions targeting the vagus nerve. This will provide valuable insights for future research on treatment of obesity and gastrointestinal and depressive disorders based on vagus nerve stimulation.

Palmitic Acid Modulation of the Insulin-Like Growth Factor System in Hypothalamic Astrocytes and Neurons

INTRODUCTION

Insulin-like growth factor (IGF)1 and IGF2 have neuroprotective effects, but less is known regarding how other members of the IGF system, including IGF binding proteins (IGFBPs) and the regulatory proteinase pappalysin-1 (PAPP-A) and its endogenous inhibitor stanniocalcin-2 (STC2) participate in this process. Here, we analyzed whether these members of the IGF system are modified in neurons and astrocytes in response to palmitic acid (PA), a fatty acid that induces cell stress when increased centrally.

METHODS

Primary hypothalamic astrocyte cultures from male and female PND2 rats and the pro-opiomelanocortin (POMC) neuronal cell line, mHypoA-POMC/GFP-2, were treated with PA, IGF1 or both. To analyze the role of STC2 in astrocytes, siRNA assays were employed.

RESULTS

In astrocytes of both sexes, PA rapidly increased cell stress factors followed by increased Pappa and Stc2 mRNA levels and then a decrease in Igf1, Igf2, and Igfbp2 expression and cell number. Exogenous IGF1 did not revert these effects. In mHypoA-POMC/GFP-2 neurons, PA reduced cell number and Pomc and Igf1 mRNA levels, and increased Igfbp2 and Stc2, again with no effect of exogenous IGF1. PA increased STC2 expression, but no effects of decreasing its levels by interference assays or exogenous STC2 treatment in astrocytes were found.

CONCLUSIONS

The response of the IGF system to PA was cell and sex specific, but no protective effects of the IGFs were found. However, the modifications in hypothalamic PAPP-A and STC2 indicate that further studies are required to determine their role in the response to fatty acids and possibly in metabolic control.

Extracellular vesicles released from microglia after palmitate exposure impact brain function

Dietary patterns that include an excess of foods rich in saturated fat are associated with brain dysfunction. Although microgliosis has been proposed to play a key role in the development of brain dysfunction in diet-induced obesity (DIO), neuroinflammation with cytokine over-expression is not always observed. Thus, mechanisms by which microglia contribute to brain impairment in DIO are uncertain. Using the BV2 cell model, we investigated the gliosis profile of microglia exposed to palmitate (200 µmol/L), a saturated fatty acid abundant in high-fat diet and in the brain of obese individuals. We observed that microglia respond to a 24-hour palmitate exposure with increased proliferation, and with a metabolic network rearrangement that favors energy production from glycolysis rather than oxidative metabolism, despite stimulated mitochondria biogenesis. In addition, while palmitate did not induce increased cytokine expression, it modified the protein cargo of released extracellular vesicles (EVs). When administered intra-cerebroventricularly to mice, EVs secreted from palmitate-exposed microglia in vitro led to memory impairment, depression-like behavior, and glucose intolerance, when compared to mice receiving EVs from vehicle-treated microglia. We conclude that microglia exposed to palmitate can mediate brain dysfunction through the cargo of shed EVs.

Microglia mediate the early-life programming of adult glucose control

Mammalian glucose homeostasis is, in part, nutritionally programmed during early neonatal life, a critical window for the formation of synapses between hypothalamic glucoregulatory centers. Although microglia are known to prune synapses throughout the brain, their specific role in refining hypothalamic glucoregulatory circuits remains unknown. Here, we show that microglia in the mediobasal hypothalamus (MBH) of mice actively engage in synaptic pruning during early life. Microglial phagocytic activity is induced following birth, regresses upon weaning from maternal milk, and is exacerbated by feeding dams a high-fat diet while lactating. In particular, we show that microglia refine perineuronal nets (PNNs) within the neonatal MBH. Indeed, transiently depleting microglia before weaning (P6-16), but not afterward (P21-31), remarkably increased PNN abundance in the MBH. Furthermore, mice lacking microglia only from P6-16 had glucose intolerance due to impaired glucose-responsive pancreatic insulin secretion in adulthood, a phenotype not seen if microglial depletion occurred after weaning. Viral retrograde tracing revealed that this impairment is linked to a reduction in the number of neurons in specific hypothalamic glucoregulatory centers that synaptically connect to the pancreatic β-cell compartment. These findings show that microglia facilitate synaptic plasticity in the MBH during early life through a process that includes PNN refinement, to establish hypothalamic circuits that regulate adult glucose homeostasis.

Microglia Morphological Response to Mesenchymal Stromal Cell Extracellular Vesicles Demonstrates EV Therapeutic Potential for Modulating Neuroinflammation

Background

Mesenchymal stromal cell derived extracellular vesicles (MSC-EVs) are a promising therapeutic for neuroinflammation. MSC-EVs can interact with microglia, the resident immune cells of the brain, to exert their immunomodulatory effects. In response to inflammatory cues, such as cytokines, microglia undergo phenotypic changes indicative of their function e.g. morphology and secretion. However, these changes in response to MSC-EVs are not well understood. Additionally, no disease-relevant screening tools to assess MSC-EV bioactivity exist, which has further impeded clinical translation. Here, we developed a quantitative, high throughput morphological profiling approach to assess the response of microglia to neuroinflammation-relevant signals and whether this morphological response can be used to indicate the bioactivity of MSC-EVs.

Results

Using an immortalized human microglia cell-line, we observed increased size (perimeter, major axis length) and complexity (form factor) upon stimulation with interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α). Upon treatment with MSC-EVs, the overall morphological score (determined using principal component analysis) shifted towards the unstimulated morphology, indicating that MSC-EVs are bioactive and modulate microglia. The morphological effects of MSC-EVs in TNF-γ/IFN-α stimulated cells were concomitant with reduced secretion of 14 chemokines/cytokines (e.g. CXCL6, CXCL9) and increased secretion of 12 chemokines/cytokines (e.g. CXCL8, CXCL10). Proteomic analysis of cell lysates revealed significant increases in 192 proteins (e.g. HIBADH, MEAK7, LAMC1) and decreases in 257 proteins (e.g. PTEN, TOM1, MFF) with MSC-EV treatment. Of note, many of these proteins are involved in regulation of cell morphology and migration. Gene Set Variation Analysis revealed upregulation of pathways associated with immune response, such as regulation of cytokine production, immune cell infiltration (e.g. T cells, NK cells) and morphological changes (e.g. Semaphorin, RHO/Rac signaling). Additionally, changes in microglia mitochondrial morphology were measured suggesting that MSC-EV modulate mitochondrial metabolism.

Conclusion

This study comprehensively demonstrates the effects of MSC-EVs on human microglial morphology, cytokine secretion, cellular proteome, and mitochondrial content. Our high-throughput, rapid, low-cost morphological approach enables screening of MSC-EV batches and manufacturing conditions to enhance EV function and mitigate EV functional heterogeneity in a disease relevant manner. This approach is highly generalizable and can be further adapted and refined based on selection of the disease-relevant signal, target cell, and therapeutic product.

Hypothalamic Inflammation Improves Through Bariatric Surgery, and Hypothalamic Volume Predicts Short-Term Weight Loss Response in Adults With or Without Type 2 Diabetes

OBJECTIVE

Preclinical research implicates hypothalamic inflammation (HI) in obesity and type 2 diabetes pathophysiology. However, their pathophysiological relevance and potential reversibility need to be better defined. We sought to evaluate the effect of bariatric surgery (BS) on radiological biomarkers of HI and the association between the severity of such radiological alterations and post-BS weight loss (WL) trajectories. The utility of cerebrospinal fluid large extracellular vesicles (CSF-lEVs) enriched for microglial and astrocyte markers in studying HI was also explored.

RESEARCH DESIGN AND METHODS

We included 72 individuals with obesity (20 with and 52 without type 2 diabetes) and 24 control individuals. Participants underwent lumbar puncture and 3-T MRI at baseline and 1-year post-BS. We assessed hypothalamic mean diffusivity (MD) (higher values indicate lesser microstructural integrity) and the volume of the whole and main hypothalamic subregions. CSF-lEVs enriched for glial and astrocyte markers were determined by flow cytometry.

RESULTS

Compared with control group, the obesity and type 2 diabetes groups showed a larger volume and higher MD in the hypothalamic tubular inferior region, the area encompassing the arcuate nucleus. These radiological alterations were positively associated with baseline anthropometric and metabolic measures and improved post-BS. A larger baseline tubular inferior hypothalamic volume was independently related to lesser WL 1 and 2 years after BS. CSF-lEVs did not differ among groups and were unrelated to WL trajectories.

CONCLUSIONS

These findings suggest HI improvement after BS and may support a role for HI in modulating the WL response to these interventions.

Obesity-induced inflammation: connecting the periphery to the brain

Obesity is often associated with a chronic, low-grade inflammatory state affecting the entire body. This sustained inflammatory state disrupts the coordinated communication between the periphery and the brain, which has a crucial role in maintaining homeostasis through humoural, nutrient-mediated, immune and nervous signalling pathways. The inflammatory changes induced by obesity specifically affect communication interfaces, including the blood-brain barrier, glymphatic system and meninges. Consequently, brain areas near the third ventricle, including the hypothalamus and other cognition-relevant regions, become susceptible to impairments, resulting in energy homeostasis dysregulation and an elevated risk of cognitive impairments such as Alzheimer's disease and dementia. This Review explores the intricate communication between the brain and the periphery, highlighting the effect of obesity-induced inflammation on brain function.

Synergism Between Hypothalamic Astrocytes and Neurons in Metabolic Control

Astrocytes are no longer considered as passive support cells. In the hypothalamus, these glial cells actively participate in the control of appetite, energy expenditure, and the processes leading to obesity and its secondary complications. Here we briefly review studies supporting this conclusion and the advances made in understanding the underlying mechanisms.

Elevated interleukin-6 in women with binge-eating spectrum disorders

OBJECTIVE

Binge-eating spectrum disorders (BESD) involve large eating episodes accompanied by a sense of loss of control that occur in individuals with body weights spanning the full body mass index (BMI) spectrum. While research links BESD with peripheral inflammation, this literature is limited by underpowered studies and a failure to control for confounding variables that could promote inflammation independent of dysregulated eating, specifically elevated body adiposity and depression. Our study examined plasma interleukin-6 (IL-6), a marker of peripheral inflammation, in a sample of women with BESD and non-eating disorder controls, controlling for BMI, body adiposity, and depression.

METHOD

Participants (N = 94) included women with BESD (n = 73) or no eating disorder (n = 21) who completed structured clinical interviews in a larger study, selected to represent BMI categories ranging from underweight to obese in both groups. Fasting blood samples were processed for plasma IL-6 concentration via enzyme-linked immunosorbent assays. In addition to assessing group differences in plasma IL-6, exploratory analyses examined associations between IL-6 and biological and clinical markers of BESD.

RESULTS

Significantly elevated plasma IL-6 was found in women with BESD, relative to controls, that was not accounted for by BMI, adiposity, or depression. Plasma IL-6 was positively correlated with plasma leptin concentration, clinical assessments of eating disorder severity, and participants' largest self-reported eating episode.

DISCUSSION

Peripheral inflammation is specifically linked to presence of dysregulated eating independently from weight, adiposity, and depression in BESD. Future research should probe the potential role of neuroinflammation in altered eating behavior.

PUBLIC SIGNIFICANCE

This study provides the first demonstration that inflammation, characterized by elevated plasma IL-6 concentration, is uniquely associated with dysregulated eating in a transdiagnostic group of individuals with BESD. A better understanding of whether immune factors contribute to dysregulated eating could help identify novel biological targets for intervention.

High-fat diet consumption promotes adolescent neurobehavioral abnormalities and hippocampal structural alterations via microglial overactivation accompanied by an elevated serum free fatty acid concentration

Mounting evidence suggests that high-fat diet (HFD) consumption increases the risk for depression, but the neurophysiological mechanisms involved remain to be elucidated. Here, we demonstrated that HFD feeding of C57BL/6J mice during the adolescent period (from 4 to 8 weeks of age) resulted in increased depression- and anxiety-like behaviors concurrent with changes in neuronal and myelin structure in the hippocampus. Additionally, we showed that hippocampal microglia in HFD-fed mice assumed a hyperactive state concomitant with increased PSD95-positive and myelin basic protein (MBP)-positive inclusions, implicating microglia in hippocampal structural alterations induced by HFD consumption. Along with increased levels of serum free fatty acids (FFAs), abnormal deposition of lipid droplets and increased levels of HIF-1α protein (a transcription factor that has been reported to facilitate cellular lipid accumulation) within hippocampal microglia were observed in HFD-fed mice. The use of minocycline, a pharmacological suppressor of microglial overactivation, effectively attenuated neurobehavioral abnormalities and hippocampal structural alterations but barely altered lipid droplet accumulation in the hippocampal microglia of HFD-fed mice. Coadministration of triacsin C abolished the increases in lipid droplet formation, phagocytic activity, and ROS levels in primary microglia treated with serum from HFD-fed mice. In conclusion, our studies demonstrate that the adverse influence of early-life HFD consumption on behavior and hippocampal structure is attributed at least in part to microglial overactivation that is accompanied by an elevated serum FFA concentration and microglial aberrations represent a potential preventive and therapeutic target for HFD-related emotional disorders.

Breast cancer exploits neural signaling pathways for bone-to-meninges metastasis

The molecular mechanisms that regulate breast cancer cell (BCC) metastasis and proliferation within the leptomeninges (LM) are poorly understood, which limits the development of effective therapies. In this work, we show that BCCs in mice can invade the LM by abluminal migration along blood vessels that connect vertebral or calvarial bone marrow and meninges, bypassing the blood-brain barrier. This process is dependent on BCC engagement with vascular basement membrane laminin through expression of the neuronal pathfinding molecule integrin α6. Once in the LM, BCCs colocalize with perivascular meningeal macrophages and induce their expression of the prosurvival neurotrophin glial-derived neurotrophic factor (GDNF). Intrathecal GDNF blockade, macrophage-specific GDNF ablation, or deletion of the GDNF receptor neural cell adhesion molecule (NCAM) from BCCs inhibits breast cancer growth within the LM. These data suggest integrin α6 and the GDNF signaling axis as new therapeutic targets against breast cancer LM metastasis.

Mechanisms of inflammation after ischemic stroke in brain-peripheral crosstalk

Stroke is a devastating disease with high morbidity, disability, and mortality, among which ischemic stroke is more common. However, there is still a lack of effective methods to improve the prognosis and reduce the incidence of its complications. At present, there is evidence that peripheral organs are involved in the inflammatory response after stroke. Moreover, the interaction between central and peripheral inflammation includes the activation of resident and peripheral immune cells, as well as the activation of inflammation-related signaling pathways, which all play an important role in the pathophysiology of stroke. In this review, we discuss the mechanisms of inflammatory response after ischemic stroke, as well as the interactions through circulatory pathways between peripheral organs (such as the gut, heart, lung and spleen) and the brain to mediate and regulate inflammation after ischemic stroke. We also propose the potential role of meningeal lymphatic vessels (MLVs)-cervical lymph nodes (CLNs) as a brain-peripheral crosstalk lymphatic pathway in ischemic stroke. In addition, we also summarize the mechanisms of anti-inflammatory drugs in the treatment of ischemic stroke.

Inflammation as a Sex-Specific Mediator in the Relationship between Maternal and Offspring Obesity in C57Bl/6J Mice

Maternal obesity is a well-established risk factor for offspring obesity development. The relationship between maternal and offspring obesity is mediated in part by developmental programming of offspring metabolic circuitry, including hypothalamic signaling. Dysregulated hypothalamic inflammation has also been linked to development of obesity. We utilized an established C57Bl/6J mouse model of high-fat, high-sugar diet induced maternal obesity to evaluate the effect of maternal obesity on systemic and hypothalamic TNF-α, IL-6, and IL-1β levels in neonatal and adult offspring. The offspring of dams with obesity demonstrated increased adiposity and decreased activity compared to control offspring. Maternal obesity was associated with decreased plasma TNF-α, IL-6 and IL-1β in adult female offspring and decreased plasma IL-6 in neonatal male offspring. Neonatal female offspring of obese dams had decreased TNF-α gene expression in the hypothalamus compared to control females, while neonatal and adult male offspring of obese dams had decreased IL-6 gene expression in the hypothalamus compared to control males. In summary, our results highlight important sex differences in the inflammatory phenotype of offspring exposed to maternal obesity. Sex-specific immunomodulatory mechanisms should be considered in future efforts to develop therapeutic interventions for obesity prevention and treatment.

Childhood Obesity, Hypothalamic Inflammation, and the Onset of Puberty: A Narrative Review

The onset of puberty, which is under the control of the hypothalamic-pituitary-gonadal (HPG) axis, is influenced by various factors, including obesity, which has been associated with the earlier onset of puberty. Obesity-induced hypothalamic inflammation may cause premature activation of gonadotropin-releasing hormone (GnRH) neurons, resulting in the development of precocious or early puberty. Mechanisms involving phoenixin action and hypothalamic microglial cells are implicated. Furthermore, obesity induces structural and cellular brain alterations, disrupting metabolic regulation. Imaging studies reveal neuroinflammatory changes in obese individuals, impacting pubertal timing. Magnetic resonance spectroscopy enables the assessment of the brain's neurochemical composition by measuring key metabolites, highlighting potential pathways involved in neurological changes associated with obesity. In this article, we present evidence indicating a potential association among obesity, hypothalamic inflammation, and precocious puberty.

Network pharmacology combined with lipidomics to reveal the regulatory effects and mechanisms of Kangzao granules in the hypothalamus of rats with central precocious puberty

Central precocious puberty (CPP) is a prevalent endocrine disorder that primarily affects children, specifically females, and is associated with various physical and psychological complications. Although Kangzao granules (KZG) are efficacious in managing CPP, the underlying mechanisms remain unclear. Therefore, this study aimed to elucidate the therapeutic mechanisms of KZG using network pharmacology, molecular docking, pharmacodynamics, and pathway validation. A putative compound-target-pathway network was constructed using Cytoscape, before KEGG and Gene Ontology enrichment analyses were conducted. Moreover, molecular docking was performed using AutoDockTools. Quality control of the 10 key components of KZG was carried out using UHPLC-ESI/LTQ-Orbitrap-MS/MS, and hypothalamic lipids were analyzed using UHPLC-Q-Exactive Orbitrap MS/MS. In total, 87 bioactive compounds that targeting 110 core proteins to alleviate CPP were identified in KZG. Lipidomic analysis revealed 18 differential lipids among the CPP, KZG, and control groups, wherein fatty acids were significantly reduced in the model group; however, these changes were effectively counteracted by KZG treatment. Molecular docking analysis revealed a strong binding affinity between flavonoids and RAC-alpha serine/threonine-protein kinase (AKT) when docked into the crystal structure. Moreover, a substantial disruption in lipid metabolism was observed in the model group; however, treatment with KZG efficiently reversed these alterations. Furthermore, the phosphoinositide 3-kinase/AKT signaling pathway was identified as a pivotal regulator of hypothalamic lipid metabolism regulator. Overall, this study highlights the effectiveness of a multidisciplinary approach that combines network pharmacology, lipidomics, molecular docking, and experimental validation in the elucidation of the therapeutic mechanisms of KZG in CPP treatment.

Interaction of high-fat diet and brain trauma alters adipose tissue macrophages and brain microglia associated with exacerbated cognitive dysfunction

Obesity increases the morbidity and mortality of traumatic brain injury (TBI). Detailed analyses of transcriptomic changes in the brain and adipose tissue were performed to elucidate the interactive effects between high-fat diet-induced obesity (DIO) and TBI. Adult male mice were fed a high-fat diet (HFD) for 12 weeks prior to experimental TBI and continuing after injury. High-throughput transcriptomic analysis using Nanostring panels of the total visceral adipose tissue (VAT) and cellular components in the brain, followed by unsupervised clustering, principal component analysis, and IPA pathway analysis were used to determine shifts in gene expression patterns and molecular pathway activity. Cellular populations in the cortex and hippocampus, as well as in VAT, during the chronic phase after combined TBI-HFD showed amplification of central and peripheral microglia/macrophage responses, including superadditive changes in selected gene expression signatures and pathways. Furthermore, combined TBI and HFD caused additive dysfunction in Y-Maze, Novel Object Recognition (NOR), and Morris water maze (MWM) cognitive function tests. These novel data suggest that HFD-induced obesity and TBI can independently prime and support the development of altered states in brain microglia and VAT, including the disease-associated microglia/macrophage (DAM) phenotype observed in neurodegenerative disorders. The interaction between HFD and TBI promotes a shift toward chronic reactive microglia/macrophage transcriptomic signatures and associated pro-inflammatory disease-altered states that may, in part, underlie the exacerbation of cognitive deficits. Thus, targeting of HFD-induced reactive cellular phenotypes, including in peripheral adipose tissue immune cell populations, may serve to reduce microglial maladaptive states after TBI, attenuating post-traumatic neurodegeneration and neurological dysfunction.

An acute microglial metabolic response controls metabolism and improves memory

Chronic high-fat feeding triggers chronic metabolic dysfunction including obesity, insulin resistance, and diabetes. How high-fat intake first triggers these pathophysiological states remains unknown. Here, we identify an acute microglial metabolic response that rapidly translates intake of high-fat diet (HFD) to a surprisingly beneficial effect on metabolism and spatial / learning memory. High-fat intake rapidly increases palmitate levels in cerebrospinal fluid and triggers a wave of microglial metabolic activation characterized by mitochondrial membrane activation and fission as well as metabolic skewing towards aerobic glycolysis. These effects are detectable throughout the brain and can be detected within as little as 12 hours of HFD exposure. In vivo, microglial ablation and conditional DRP1 deletion show that the microglial metabolic response is necessary for the acute effects of HFD. 13C-tracing experiments reveal that in addition to processing via β-oxidation, microglia shunt a substantial fraction of palmitate towards anaplerosis and re-release of bioenergetic carbons into the extracellular milieu in the form of lactate, glutamate, succinate, and intriguingly, the neuro-protective metabolite itaconate. Together, these data identify microglia as a critical nutrient regulatory node in the brain, metabolizing away harmful fatty acids and releasing the same carbons as alternate bioenergetic and protective substrates for surrounding cells. The data identify a surprisingly beneficial effect of short-term HFD on learning and memory.

A review of air pollution as a driver of cardiovascular disease risk across the diabetes spectrum

The prevalence of diabetes is estimated to reach almost 630 million cases worldwide by the year 2045; of current and projected cases, over 90% are type 2 diabetes. Air pollution exposure has been implicated in the onset and progression of diabetes. Increased exposure to fine particulate matter air pollution (PM2.5) is associated with increases in blood glucose and glycated hemoglobin (HbA1c) across the glycemic spectrum, including normoglycemia, prediabetes, and all forms of diabetes. Air pollution exposure is a driver of cardiovascular disease onset and exacerbation and can increase cardiovascular risk among those with diabetes. In this review, we summarize the literature describing the relationships between air pollution exposure, diabetes and cardiovascular disease, highlighting how airborne pollutants can disrupt glucose homeostasis. We discuss how air pollution and diabetes, via shared mechanisms leading to endothelial dysfunction, drive increased cardiovascular disease risk. We identify portable air cleaners as potentially useful tools to prevent adverse cardiovascular outcomes due to air pollution exposure across the diabetes spectrum, while emphasizing the need for further study in this particular population. Given the enormity of the health and financial impacts of air pollution exposure on patients with diabetes, a greater understanding of the interventions to reduce cardiovascular risk in this population is needed.

The molecular mechanism of macrophage-adipocyte crosstalk in maintaining energy homeostasis

Interactions between macrophages and adipocytes in adipose tissue are critical for the regulation of energy metabolism and obesity. Macrophage polarization induced by cold or other stimulations can drive metabolic reprogramming of adipocytes, browning, and thermogenesis. Accordingly, investigating the roles of macrophages and adipocytes in the maintenance of energy homeostasis is critical for the development of novel therapeutic approaches specifically targeting macrophages in metabolic disorders such as obesity. Current review outlines macrophage polarization not only regulates the release of central nervous system and inflammatory factors, but controls mitochondrial function, and other factor that induce metabolic reprogramming of adipocytes and maintain energy homeostasis. We also emphasized on how the adipocytes conversely motivate the polarization of macrophage. Exploring the interactions between adipocytes and macrophages may provide new therapeutic strategies for the management of obesity-related metabolic diseases.

Endocrine Disruptors and Metabolic Changes: Impact on Puberty Control

OBJECTIVE

This study aims to explore the significant impact of environmental chemicals on disease development, focusing on their role in developing metabolic and endocrine diseases. The objective is to understand how these chemicals contribute to the increasing prevalence of precocious puberty, considering various factors, including epigenetic changes, lifestyle, and emotional disturbances.

METHODS

The study employs a comprehensive review of descriptive observational studies in both human and animal models to identify a degree of causality between exposure to environmental chemicals and disease development, specifically focusing on endocrine disruption. Due to ethical constraints, direct causation studies in human subjects are not feasible; therefore, the research relies on accumulated observational data.

RESULTS

Puberty is a crucial life period with marked physiological and psychological changes. The age at which sexual characteristics develop is changing in many regions. The findings indicate a correlation between exposure to endocrine-disrupting chemicals and the early onset of puberty. These chemicals have been shown to interfere with normal hormonal processes, particularly during critical developmental stages such as adolescence. The research also highlights the interaction of these chemical exposures with other factors, including nutritional history, social and lifestyle changes, and emotional stress, which together contribute to the prevalence of precocious puberty.

CONCLUSION

Environmental chemicals significantly contribute to the development of certain metabolic and endocrine diseases, particularly in the rising incidence of precocious puberty. Although the evidence is mainly observational, it adequately justifies regulatory actions to reduce exposure risks. Furthermore, these findings highlight the urgent need for more research on the epigenetic effects of these chemicals and their wider impact on human health, especially during vital developmental periods.

Hypothalamic astrocyte NAD+ salvage pathway mediates the coupling of dietary fat overconsumption in a mouse model of obesity

Nicotinamide adenine dinucleotide (NAD)+ serves as a crucial coenzyme in numerous essential biological reactions, and its cellular availability relies on the activity of the nicotinamide phosphoribosyltransferase (NAMPT)-catalyzed salvage pathway. Here we show that treatment with saturated fatty acids activates the NAD+ salvage pathway in hypothalamic astrocytes. Furthermore, inhibition of this pathway mitigates hypothalamic inflammation and attenuates the development of obesity in male mice fed a high-fat diet (HFD). Mechanistically, CD38 functions downstream of the NAD+ salvage pathway in hypothalamic astrocytes burdened with excess fat. The activation of the astrocytic NAMPT-NAD+-CD38 axis in response to fat overload induces proinflammatory responses in the hypothalamus. It also leads to aberrantly activated basal Ca2+ signals and compromised Ca2+ responses to metabolic hormones such as insulin, leptin, and glucagon-like peptide 1, ultimately resulting in dysfunctional hypothalamic astrocytes. Our findings highlight the significant contribution of the hypothalamic astrocytic NAD+ salvage pathway, along with its downstream CD38, to HFD-induced obesity.

Dietary fatty acid composition drives neuroinflammation and impaired behavior in obesity

Nutrient composition in obesogenic diets may influence the severity of disorders associated with obesity such as insulin-resistance and chronic inflammation. Here we hypothesized that obesogenic diets rich in fat and varying in fatty acid composition, particularly in omega 6 (ω6) to omega 3 (ω3) ratio, have various effects on energy metabolism, neuroinflammation and behavior. Mice were fed either a control diet or a high fat diet (HFD) containing either low (LO), medium (ME) or high (HI) ω6/ω3 ratio. Mice from the HFD-LO group consumed less calories and exhibited less body weight gain compared to other HFD groups. Both HFD-ME and HFD-HI impaired glucose metabolism while HFD-LO partly prevented insulin intolerance and was associated with normal leptin levels despite higher subcutaneous and perigonadal adiposity. Only HFD-HI increased anxiety and impaired spatial memory, together with increased inflammation in the hypothalamus and hippocampus. Our results show that impaired glucose metabolism and neuroinflammation are uncoupled, and support that diets with a high ω6/ω3 ratio are associated with neuroinflammation and the behavioral deterioration coupled with the consumption of diets rich in fat.

Reversal of High Fat Diet-Induced Obesity, Systemic Inflammation, and Astrogliosis by the NLRP3 Inflammasome Inhibitors NT-0249 and NT-0796

Systemic and cerebral inflammatory responses are implicated in the pathogenesis of obesity and associated metabolic impairment. While the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome has been linked to obesity-associated inflammation, whether it contributes to the development or maintenance of obesity is unknown. We provide support for a direct role of saturated fatty acids, such as palmitic acid, as NLRP3 activating stimuli in obese states. To investigate whether NLRP3 activation contributes to the pathogenesis of diet-induced obesity (DIO) in mice, we tested two different clinical-stage NLRP3 inflammasome inhibitors. We demonstrate a contributory role of this key inflammasome to established obesity and associated systemic and cerebral inflammation. By comparing their effects to calorie restriction, we aimed to identify specific NLRP3-sensitive mechanisms contributing to obesity-induced inflammation (as opposed to be those regulated by weight loss per se). In addition, a direct comparison of an NLRP3 inhibitor to a glucagon like peptide-1 receptor agonist, semaglutide (Wegovy), in the DIO model allowed an appreciation of the relative efficacy of these two therapeutic strategies on obesity, its associated systemic inflammatory response, and cerebral gliosis. We show that two structurally distinct, NLRP3 inhibitors, NT-0249 and NT-0796, reverse obesity in the DIO mouse model and that brain exposure appears necessary for efficacy. In support of this, we show that DIO-driven hypothalamic glial fibrillary acidic protein expression is blocked by dosing with NT-0249/NT-0796. While matching weight loss driven by semaglutide or calorie restriction, remarkably, NLRP3 inhibition provided enhanced improvements in disease-relevant biomarkers of acute phase response, cardiovascular inflammation, and lipid metabolism. SIGNIFICANCE STATEMENT: Obesity is a global health concern that predisposes individuals to chronic disease such as diabetes and cardiovascular disease at least in part by promoting systemic inflammation. We report that in mice fed a high-fat, obesogenic diet, obesity is reversed by either of two inhibitors of the intracellular inflammatory mediator NLRP3. Furthermore, NLRP3 inhibition reduces both hypothalamic gliosis and circulating biomarkers of cardiovascular disease risk beyond what can be achieved by either the glucagon like peptide-1 agonist semaglutide or calorie restriction alone.

Microglia/macrophage-specific deletion of TLR-4 protects against neural effects of diet-induced obesity

Obesity is associated with numerous adverse neural effects, including reduced neurogenesis, cognitive impairment, and increased risks for developing Alzheimer's disease (AD) and vascular dementia. Obesity is also characterized by chronic, low-grade inflammation that is implicated in mediating negative consequences body-wide. Toll-like receptor 4 (TLR4) signaling from peripheral macrophages is implicated as an essential regulator of the systemic inflammatory effects of obesity. In the brain, obesity drives chronic neuroinflammation that involves microglial activation, however the contributions of microglia-derived TLR4 signaling to the consequences of obesity are poorly understood. To investigate this issue, we first generated mice that carry an inducible, microglia/macrophage-specific deletion of TLR4 that yields long-term TLR4 knockout only in brain indicating microglial specificity. Next, we analyzed the effects of microglial TLR4 deletion on systemic and neural effects of a 16-week of exposure to control versus obesogenic high-fat diets. In male mice, TLR4 deletion generally yielded limited effects on diet-induced systemic metabolic dysfunction but significantly reduced neuroinflammation and impairments in neurogenesis and cognitive performance. In female mice maintained on obesogenic diet, TLR4 deletion partially protected against weight gain, adiposity, and metabolic impairments. Compared to males, females showed milder diet-induced neural consequences, against which TLR4 deletion was protective. Collectively, these findings demonstrate a central role of microglial TLR4 signaling in mediating the neural effects of obesogenic diet and highlight sexual dimorphic responses to both diet and TLR4.

Perinatal Western-style diet exposure associated with decreased microglial counts throughout the arcuate nucleus of the hypothalamus in Japanese macaques

Perinatal exposure to a high-fat, high-sugar Western-style diet (WSD) is associated with altered neural circuitry in the melanocortin system. This association may have an underlying inflammatory component, as consumption of a WSD during pregnancy can lead to an elevated inflammatory environment. Our group previously demonstrated that prenatal WSD exposure was associated with increased markers of inflammation in the placenta and fetal hypothalamus in Japanese macaques. In this follow-up study, we sought to determine whether this heightened inflammatory state persisted into the postnatal period, as prenatal exposure to inflammation has been shown to reprogram offspring immune function and long-term neuroinflammation would present a potential means for prolonged disruptions to microglia-mediated neuronal circuit formation. Neuroinflammation was approximated in 1-yr-old offspring by counting resident microglia and peripherally derived macrophages in the region of the hypothalamus examined in the fetal study, the arcuate nucleus (ARC). Microglia and macrophages were immunofluorescently stained with their shared marker, ionized calcium-binding adapter molecule 1 (Iba1), and quantified in 11 regions along the rostral-caudal axis of the ARC. A mixed-effects model revealed main effects of perinatal diet (P = 0.011) and spatial location (P = 0.003) on Iba1-stained cell count. Perinatal WSD exposure was associated with a slight decrease in the number of Iba1-stained cells, and cells were more densely located in the center of the ARC. These findings suggest that the heightened inflammatory state experienced in utero does not persist postnatally. This inflammatory response trajectory could have important implications for understanding how neurodevelopmental disorders progress.NEW & NOTEWORTHY Prenatal Western-style diet exposure is associated with increased microglial activity in utero. However, we found a potentially neuroprotective reduction in microglia count during early postnatal development. This trajectory could inform the timing of disruptions to microglia-mediated neuronal circuit formation. Additionally, this is the first study in juvenile macaques to characterize the distribution of microglia along the rostral-caudal axis of the arcuate nucleus of the hypothalamus. Nearby neuronal populations may be greater targets during inflammatory insults.

Microgliosis: a double-edged sword in the control of food intake

Maintaining energy balance is essential for survival and health. This physiological function is controlled by the brain, which adapts food intake to energy needs. Indeed, the brain constantly receives a multitude of biological signals that are derived from digested foods or that originate from the gastrointestinal tract, energy stores (liver and adipose tissues) and other metabolically active organs (muscles). These signals, which include circulating nutrients, hormones and neuronal inputs from the periphery, collectively provide information on the overall energy status of the body. In the brain, several neuronal populations can specifically detect these signals. Nutrient-sensing neurons are found in discrete brain areas and are highly enriched in the hypothalamus. In turn, specialized brain circuits coordinate homeostatic responses acting mainly on appetite, peripheral metabolism, activity and arousal. Accumulating evidence shows that hypothalamic microglial cells located at the vicinity of these circuits can influence the brain control of energy balance. However, microglial cells could have opposite effects on energy balance, that is homeostatic or detrimental, and the conditions for this shift are not totally understood yet. One hypothesis relies on the extent of microglial activation, and nutritional lipids can considerably change it.

White-brown adipose tissue interplay in polycystic ovary syndrome: Therapeutic avenues

This study highlights the therapeutic potential of activating brown adipose tissue (BAT) for managing polycystic ovary syndrome (PCOS), a prevalent endocrine disorder associated with metabolic and reproductive abnormalities. BAT plays a crucial role in regulating energy expenditure and systemic insulin sensitivity, making it an attractive target for the treatment of obesity and metabolic diseases. Recent research suggests that impaired BAT function and mass may contribute to the link between metabolic disturbances and reproductive issues in PCOS. Additionally, abnormal white adipose tissue (WAT) can exacerbate these conditions by releasing adipokines and nonesterified fatty acids. In this review, we explored the impact of WAT changes on BAT function in PCOS and discussed the potential of BAT activation as a therapeutic strategy to improve PCOS symptoms. We propose that BAT activation holds promise for managing PCOS; however, further research is needed to confirm its efficacy and to develop clinically feasible methods for BAT activation.

Maternal Western diet programs cardiometabolic dysfunction and hypothalamic inflammation via epigenetic mechanisms predominantly in the male offspring

OBJECTIVE

Maternal exposure during pregnancy is a strong determinant of offspring health outcomes. Such exposure induces changes in the offspring epigenome resulting in gene expression and functional changes. In this study, we investigated the effect of maternal Western hypercaloric diet (HCD) programming during the perinatal period on neuronal plasticity and cardiometabolic health in adult offspring.

METHODS

C57BL/6J dams were fed HCD for 1 month prior to mating with regular diet (RD) sires and kept on the same diet throughout pregnancy and lactation. At weaning, offspring were maintained on either HCD or RD for 3 months resulting in 4 treatment groups that underwent cardiometabolic assessments. DNA and RNA were extracted from the hypothalamus to perform whole genome methylation, mRNA, and miRNA sequencing followed by bioinformatic analyses.

RESULTS

Maternal programming resulted in male-specific hypertension and hyperglycemia, with both males and females showing increased sympathetic tone to the vasculature. Surprisingly, programmed male offspring fed HCD in adulthood exhibited lower glucose levels, less insulin resistance, and leptin levels compared to non-programmed HCD-fed male mice. Hypothalamic genes involved in inflammation and type 2 diabetes were targeted by differentially expressed miRNA, while genes involved in glial and astrocytic differentiation were differentially methylated in programmed male offspring. These data were supported by our findings of astrogliosis, microgliosis and increased microglial activation in programmed males in the paraventricular nucleus (PVN). Programming induced a protective effect in male mice fed HCD in adulthood, resulting in lower protein levels of hypothalamic TGFβ2, NF-κB2, NF-κBp65, Ser-pIRS1, and GLP1R compared to non-programmed HCD-fed males. Although TGFβ2 was upregulated in male mice exposed to HCD pre- or post-natally, only blockade of the brain TGFβ receptor in RD-HCD mice improved glucose tolerance and a trend to weight loss.

CONCLUSIONS

Our study shows that maternal HCD programs neuronal plasticity in the offspring and results in male-specific hypertension and hyperglycemia associated with hypothalamic inflammation in mechanisms and pathways distinct from post-natal HCD exposure. Together, our data unmask a compensatory role of HCD programming, likely via priming of metabolic pathways to handle excess nutrients in a more efficient way.

Important roles of linoleic acid and α-linolenic acid in regulating cognitive impairment and neuropsychiatric issues in metabolic-related dementia

Metabolic syndrome (MetS), which is characterized by insulin resistance, high blood glucose, obesity, and dyslipidemia, is known to increase the risk of dementia accompanied by memory loss and depression. The direct pathways and specific mechanisms in the central nervous system (CNS) for addressing fatty acid imbalances in MetS have not yet been fully elucidated. Among polyunsaturated acids, linoleic acid (LA, n6-PUFA) and α-linolenic acid (ALA, n3-PUFA), which are two essential fatty acids that should be provided by food sources (e.g., vegetable oils and seeds), have been reported to regulate various cellular mechanisms including apoptosis, inflammatory responses, mitochondrial biogenesis, and insulin signaling. Furthermore, inadequate intake of LA and ALA is reported to be involved in neuropathology and neuropsychiatric diseases as well as imbalanced metabolic conditions. Herein, we review the roles of LA and ALA on metabolic-related dementia focusing on insulin resistance, dyslipidemia, synaptic plasticity, cognitive function, and neuropsychiatric issues. This review suggests that LA and ALA are important fatty acids for concurrent treatment of both MetS and neurological problems.

Hypothalamic FTO promotes high-fat diet-induced leptin resistance in mice through increasing CX3CL1 expression

Long-term consumption of a high-fat diet (HFD) disrupts energy homeostasis and leads to weight gain. The fat mass and obesity-associated (FTO) gene has been consistently identified to be associated with HFD-induced obesity. The hypothalamus is crucial for regulating energy balance, and HFD-induced hypothalamic leptin resistance contributes to obesity. FTO, an N6-methyladenosine (m6A) RNA methylation regulator, may be a key mediator of leptin resistance. However, the exact mechanisms remain unclear. Therefore, the present study aims to investigate the association between FTO and leptin resistance. After HFD or standard diet (SD) feeding in male mice for 22 weeks, m6A-sequencing and western blotting assays were used to identify target genes and assess protein level, and molecular interaction changes. CRISPR/Cas9 gene knockout system was employed to investigate the potential function of FTO in leptin resistance and obesity. Our data showed that chemokine (C-X3-C motif) ligand 1 (CX3CL1) was a direct downstream target of FTO-mediated m6A modification. Furthermore, upregulation of FTO/CX3CL1 and suppressor of cytokine signaling 3 (SOCS3) in the hypothalamus impaired leptin-signal transducer and activator of transcription 3 signaling, resulting in leptin resistance and obesity. Compared to wild-type (WT) mice, FTO deficiency in leptin receptor-expressing neurons of the hypothalamus significantly inhibited the upregulation of CX3CL1 and SOCS3, and partially ameliorating leptin resistance under HFD conditions. Our findings reveal that FTO involved in the hypothalamic leptin resistance and provides novel insight into the function of FTO in the contribution to hypothalamic leptin resistance and obesity.

Stress and Microglia: A Double-edged Relationship

Microglia are highly dynamic cells and acquire different activation states to modulate their multiple functions, which are tightly regulated by the central nervous system microenvironment in which they reside. In response to stress, that is to the appearance of non-physiological signals in their vicinity, microglia will adapt their function in order to promote a return to brain homeostasis. However, when these stress signals are chronically present, microglial response may not be adapted and lead to the establishment of a pathological state. The aim of this book chapter is to examine the substantial literature around the ability of acute and chronic stressors to affect microglial structure and function, with a special focus on psychosocial and nutritional stresses. We also discuss the molecular mechanisms known to date that explain the link between exposure to stressors and microglial activation.

FTO variation and early frontostriatal brain development in children

OBJECTIVE

Common obesity-associated genetic variants at the fat mass and obesity-associated (FTO) locus have been associated with appetitive behaviors and altered structure and function of frontostriatal brain regions. The authors aimed to investigate the influence of FTO variation on frontostriatal appetite circuits in early life.

METHODS

Data were drawn from RESONANCE, a longitudinal study of early brain development. Growth trajectories of nucleus accumbens and frontal lobe volumes, as well as total gray matter and white matter volume, by risk allele (AA) carrier status on FTO single-nucleotide polymorphism rs9939609 were examined in 228 children (102 female, 126 male) using magnetic resonance imaging assessments obtained from infancy through middle childhood. The authors fit functional concurrent regression models with brain volume outcomes over age as functional responses, and FTO genotype, sex, BMI z score, and maternal education were included as predictors.

RESULTS

Bootstrap pointwise 95% CI for regression coefficient functions in the functional concurrent regression models showed that the AA group versus the group with no risk allele (TT) had greater nucleus accumbens volume (adjusted for total brain volume) in the interval of 750 to 2250 days (2-6 years).

CONCLUSIONS

These findings suggest that common genetic risk for obesity is associated with differences in early development of brain reward circuitry and argue for investigating dynamic relationships among genotype, brain, behavior, and weight throughout development.

Metabolic Control of Microglia

Microglia, immune sentinels of the central nervous system (CNS), play a critical role in maintaining its health and integrity. This chapter delves into the concept of immunometabolism, exploring how microglial metabolism shapes their diverse immune functions. It examines the impact of cell metabolism on microglia during various CNS states, including homeostasis, development, aging, and inflammation. Particularly in CNS inflammation, the chapter discusses how metabolic rewiring in microglia can initiate, resolve, or perpetuate inflammatory responses. The potential of targeting microglial metabolism as a therapeutic strategy for chronic CNS disorders with prominent innate immune cell activation is also explored.

Palmitoylation of PKCδ by ZDHHC5 in hypothalamic microglia presents as a therapeutic target for fatty liver disease

The hypothalamus plays a fundamental role in controlling lipid metabolism through neuroendocrine signals. However, there are currently no available drug targets in the hypothalamus that can effectively improve human lipid metabolism. In this study, we found that the antimalarial drug artemether (ART) significantly improved lipid metabolism by specifically inhibiting microglial activation in the hypothalamus of high-fat diet-induced mice. Mechanically, ART protects the thyrotropin-releasing hormone (TRH) neurons surrounding microglial cells from inflammatory damage and promotes the release of TRH into the peripheral circulation. As a result, TRH stimulates the synthesis of thyroid hormone (TH), leading to a significant improvement in hepatic lipid disorders. Subsequently, we employed a biotin-labeled ART chemical probe to identify the direct cellular target in microglial cells as protein kinase Cδ (PKCδ). Importantly, ART directly targeted PKCδ to inhibit its palmitoylation modification by blocking the binding of zinc finger DHHC-type palmitoyltransferase 5 (ZDHHC5), which resulted in the inhibition of downstream neuroinflammation signaling. In vivo, hypothalamic microglia-specific PKCδ knockdown markedly impaired ART-dependent neuroendocrine regulation and lipid metabolism improvement in mice. Furthermore, single-cell transcriptomics analysis in human brain tissues revealed that the level of PKCδ in microglia positively correlated with individuals who had hyperlipemia, thereby highlighting a clinical translational value. Collectively, these data suggest that the palmitoylation of microglial PKCδ in the hypothalamus plays a role in modulating peripheral lipid metabolism through hypothalamus-liver communication, and provides a promising therapeutic target for fatty liver diseases.

Microglia in Central Control of Metabolism

Beyond their role as brain immune cells, microglia act as metabolic sensors in response to changes in nutrient availability, thus playing a role in energy homeostasis. This review highlights the evidence and challenges of studying the role of microglia in metabolism regulation.

New Insights into the Relationship between Nutrition and Neuroinflammation in Alzheimer's Disease: Preventive and Therapeutic Perspectives

Neurodegenerative diseases are progressive brain disorders characterized by inexorable synaptic dysfunction and neuronal loss. Since the most consistent risk factor for developing neurodegenerative diseases is aging, the prevalence of these disorders is intended to increase with increasing life expectancy. Alzheimer's disease is the most common cause of neurodegenerative dementia, representing a significant medical, social, and economic burden worldwide. Despite growing research to reach an early diagnosis and optimal patient management, no disease-modifying therapies are currently available. Chronic neuroinflammation has been recognized as a crucial player in sustaining neurodegenerative processes, along with pathological deposition of misfolded proteins, including amyloid-β and tau protein. Modulating neuroinflammatory responses may be a promising therapeutic strategy in future clinical trials. Among factors that are able to regulate neuroinflammatory mechanisms, diet, and nutrients represent easily accessible and modifiable lifestyle components. Mediterranean diet and several nutrients, including polyphenols, vitamins, and omega-3 polyunsaturated fatty acids, can exert antioxidant and anti-inflammatory properties, impacting clinical manifestations, cognitive decline, and dementia. This review aims to provide an updated overview of the relationship between neuroinflammation, nutrition, gut microbiota, and neurodegeneration. We summarize the major studies exploring the effects of diet regimes on cognitive decline, primarily focusing on Alzheimer's disease dementia and the impact of these results on the design of ongoing clinical trials.

CerS6-dependent ceramide synthesis in hypothalamic neurons promotes ER/mitochondrial stress and impairs glucose homeostasis in obese mice

Dysregulation of hypothalamic ceramides has been associated with disrupted neuronal pathways in control of energy and glucose homeostasis. However, the specific ceramide species promoting neuronal lipotoxicity in obesity have remained obscure. Here, we find increased expression of the C16:0 ceramide-producing ceramide synthase (CerS)6 in cultured hypothalamic neurons exposed to palmitate in vitro and in the hypothalamus of obese mice. Conditional deletion of CerS6 in hypothalamic neurons attenuates high-fat diet (HFD)-dependent weight gain and improves glucose metabolism. Specifically, CerS6 deficiency in neurons expressing pro-opiomelanocortin (POMC) or steroidogenic factor 1 (SF-1) alters feeding behavior and alleviates the adverse metabolic effects of HFD feeding on insulin sensitivity and glucose tolerance. POMC-expressing cell-selective deletion of CerS6 prevents the diet-induced alterations of mitochondrial morphology and improves cellular leptin sensitivity. Our experiments reveal functions of CerS6-derived ceramides in hypothalamic lipotoxicity, altered mitochondrial dynamics, and ER/mitochondrial stress in the deregulation of food intake and glucose metabolism in obesity.

Limitations of PLX3397 as a microglial investigational tool: peripheral and off-target effects dictate the response to inflammation

Microglia, the resident macrophages of the central nervous system (CNS), play a critical role in CNS homeostasis and neuroinflammation. Pexidartinib (PLX3397), a colony-stimulating factor 1 (CSF1) receptor inhibitor, is widely used to deplete microglia, offering flexible options for both long-term depletion and highly versatile depletion-repopulation cycles. However, the potential impact of PLX3397 on peripheral (immune) cells remains controversial. Until now, the microglia-specificity of this type of compounds has not been thoroughly evaluated, particularly in the context of peripherally derived neuroinflammation. Our study addresses this gap by examining the effects of PLX3397 on immune cells in the brain, liver, circulation and bone marrow, both in homeostasis and systemic inflammation models. Intriguingly, we demonstrate that PLX3397 treatment not only influences the levels of tissue-resident macrophages, but also affects circulating and bone marrow immune cells beyond the mononuclear phagocyte system (MPS). These alterations in peripheral immune cells disrupt the response to systemic inflammation, consequently impacting the phenotype irrespective of microglial depletion. Furthermore, we observed that a lower dose of PLX3397, which does not deplete microglia, demonstrates similar (non-)MPS effects, both in the periphery and the brain, but fails to fully replicate the peripheral alterations seen in the higher doses, questioning lower doses as a 'peripheral control' strategy. Overall, our data highlight the need for caution when interpreting studies employing this compound, as it may not be suitable for specific investigation of microglial function in the presence of systemic inflammation.